First of all, "canto" is the Italian word for "song." Second, the word comes from classical Italian poetry, where poets would divide long poems up according to cantos the way that novels have chapters. So by using the word canto, Pound is definitely connecting himself to an old, old tradition of European poetry.
More specifically, the most famous poet to divide his works into cantos is Dante Alighieri, the Italian master who wrote such famous poems as Inferno (which was so awesome they made a video game out of it) and Purgatorio. In these poems, Dante follows the main character Virgil down into hell to explore the darkest depths of the human soul. So in this sense, both Pound and Alighieri are trying to express the dark side of humanity in poetic form, maybe so they can come to terms with it and find a way to make it beautiful.